[TowerTalk] perspective
n4kg@juno.com
n4kg@juno.com
Sat, 22 Jul 2000 04:19:17 -0600
N4KG response follows.
On Wed, 19 Jul 2000 "Tom Rauch" <w8ji@contesting.com> writes:
> I've been racking my brain trying to think of a way to test the
> theory that a few dB of signal makes a big difference in a contest,
> but I can't think of a way to prove or disprove it.
>
> Can anyone?
>
> 73, Tom W8JI
Many interesting opinions have been expressed on this topic.
Here are mine.
First, it is necessary to eliminate, or at least minimize,
ALL other variables.
IMHO, the BEST way to do this is to use the same operator and
station, preferably CQing only, alternating power levels at regular
time intervals, not too short and not too long, say every 10 minutes,
fairly early in the contest when potential rates are high.
Comparing two different operators and two different stations opens
up too many variables if the conditions are not carefully controlled.
The best way to do a two station comparison would be if they
had identical antennas at identical heights with identical foregrounds
and both stations were closely spaced (1 or 2 KHz on CW) and
both CQing to the same target area.
Antenna foregrounds are a VERY important consideration that
are not apparent in statistical evaluations since such data is
never reported.
Example 1: I once had a 5L10 fixed on Europe at 40 ft shooting
over my house which had an 18 ft piece of flashing 20 ft high
and approximately 100 ft in front of this beam. It was my
least effective antenna to Europe when compared to others
at the same height or higher. When I moved that same 5L10
to another tower at 45 ft. with a clear shot (open field and woods)
for several thousand feet, it immediately became my BEST
antenna to Europe.
Example 2: My power lines come across the northern
boundry of my property at a height of 20 ft or so. My towers
are lined up to the South as follows: 50 ft away,TH7 at 40 ft;
125 ft away, 5L10 at 60 ft, 200 ft away, TH6 at 80 ft. NONE
of those antennas feel very competitive to JA / SE Asia on 10M.
When the aforementioned 5L10 (380 ft from the power
lines with clear field to JA) was rotated to Asia, it immediately
becme my BEST antenna in that direction.
Conclusion: Large conductors in the path of the ground
reflection can cost several dB of lost signal.
I suggest that during Search and Pounce (S&P) operation, small
differences in power are insignificant unless you are near the
Detection Threshold for the DX station.
Proof? In the 2000 ARRL SSB DX Contest, my friend N4NO
operated S&P only using 1000 Watts output on 20, 15, 10 Meters.
N4KG operated QRP 5W output on 80,40,20,15,10 meters. At
the end of the contest, we were nearly tied around 1000 contacts.
At one point, Sunday morning on 15M, we were in synch as we
went up the band. Every time we called together, N4NO was
first to get through, but N4KG was almost always second and
I followed him right up the band for one full sweep. My contact
total was 900 on the high bands and 100 on the low bands.
This suggests that there is a fairly low number of available
DX stations who are CQing and that S&P operators will
saturate at this contact level.
It should also be noted that DX stations who CQ probably have
a lower hearing threshold that those who do not. This assumption
is based on the fact that DX stations who CQ are typically 10 to
40 (or 50 or 60) dB stronger than DX stations who ANSWER
CQ's from USA stations. I am perplexed by the huge differential.
It must have to do with very poor antennas / very low antenna
heights, poor locations (behind mountains) or fixed antennas with
nulls in my direction etc. European QRP stations are often
stronger than the large pool of 100W stations who are just
above my detection threshold!
Second, I suggest that small differences in power can make a
BIG difference in results if you are near the detection threshold
of the DX stations. This is most readily observed on 40M SSB
where AM Broadcast stations cover much of the band leaving
little clear spectrum for North American callers.
With 1KW and a dipole antenna, it is possible to work much of
the European DX but it is often a struggle and several stations
which can be easily copied may never hear you.
After installing a 2L 40M Delta loop suspended from a 20 ft boom
at 120 ft., I noticed I was able to work most European CQers
on a single call, often without even having to give my phonetics,
just a single N 4 K G and I was in the log.
On 80 / 75 Meters, atmospheric noise and path loss are the
big enemies and again, a few dB of improved signal can make
a noticable difference.
de Tom N4KG
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